Can napping boost physical and cognitive performance following partial sleep restriction? Original paper

In this randomized crossover trial, taking a nap after two nights of partial sleep restriction did not affect physical performance, but there was evidence to suggest that it benefited cognitive performance.

Whether taking a nap following partial sleep restriction improves physical and cognitive performance.

The outcomes assessed were average power, average velocity, peak velocity, and time to peak velocity for the bench press and back squat; handgrip strength; mood state, alertness, and tiredness; and cognitive function (assessed using the Stroop test).

15 men (average age of 22) with an “intermediate” chronotype (i.e., neither “early birds” nor “night owls”) and at least 1–2 years of resistance training experience.

In this randomized crossover trial, the participants underwent partial sleep restriction by only getting 4 hours of sleep from 2:30 a.m to 6:30 a.m. for two consecutive nights. On day 3, after the second night of sleep restriction, the participants did one of the following:

• Took a 60-minute nap at 1 p.m.
• Took a 30-minute nap at 1 p.m.
• Did not nap

On day 3, mood, alertness, tiredness, and cognitive performance were assessed at 7:30 a.m., 11 a.m., 2 p.m., and 5 p.m. Physical performance was assessed at 5 p.m. via handgrip strength tests and the completion of 3 repetitions using 40%, 60%, and 80% of 1-repetition maximum for the bench press and back squat, with 5 minutes of rest between sets. The conditions were separated by a washout period of 7 days.

Sleep was recorded for 7 days using actimetry before the first experimental condition to ensure all of the participants had healthy, normal sleep habits.

Napping did not affect physical performance, tiredness, alertness, or mood. The total score on the Stroop test was higher (better) in the 60-minute nap condition compared to the other two conditions.

Although athletes commonly sleep more than 7 hours per night,^[1] they often suffer from poor sleep quality and duration due to their training, competition schedules, and traveling.^[2][3]

This could result in a variety of issues because general sleep recommendations advocate that adults sleep 7–9 hours per night,^[4] and athletes might need more sleep than the general population in order to support recovery from the high amounts of physiological and psychological stress imposed by sport.

Indeed, athletes generally report needing at least 8 hours of sleep to feel well rested,^[5] and shorter sleep durations have been associated with higher levels of pretraining fatigue,^[6] as well as higher odds of losing a competition bout.^[7] Moreover, acute sleep loss (i.e., 6 hours of sleep per night or less) has been shown to impair physical performance, including measures of both anaerobic and aerobic exercise performance.^[8] Acute sleep loss also impairs cognitive performance, as demonstrated by negative effects on attention, reaction time, and other aspects of performance.^[1]

Because athletes commonly don’t sleep enough and poor sleep impairs both physical and cognitive performance, interventions that can increase total daily sleep time are of major interest. Naps are one potential intervention. The summarized study reported that taking a 30–60 minute nap after two nights of partial sleep restriction did not affect physical performance, but there was evidence to suggest that napping did improve cognitive performance.

The results of other similarly designed studies agree with some of these findings.

A meta-analysis of 22 randomized controlled trials published in 2023 reported that napping after partial sleep restriction improved cognitive and physical performance and reduced perceived fatigue.^[9] Furthermore, the reported effect size was large for all of these outcomes. Notably, napping has also been reported to improve cognitive and physical performance and reduce perceived fatigue after a normal night of sleep (i.e., without sleep restriction, approximately 7–9 hours),^[9][10] which suggests that athletes can benefit from greater amount of sleep than what is generally recommended for adults.

These data raise the question of why the summarized study failed to find any beneficial effect of napping on physical performance. Nap duration and the timing of the performance test relative to nap awakening are unlikely to explain the results, as both of these factors were in alignment with best practice guidelines,^[9] which recommend a nap duration of 30–60 minutes and that the performance test should take place at least 60 minutes from nap awakening. In the summarized study, the performance tests took place about 3–3.5 hours after nap awakening.

Napping to improve performance

Based on the results of Mesas et al., Br J Sports Med., 2023.

Another influential factor is the method used to assess physical performance. In most studies that reported a beneficial effect of napping, a 5-meter shuttle run test was used to assess physical performance,^[9][10] which is a very different task than performing a handgrip strength test and submaximal resistance exercise.

There is limited data available regarding the effects of napping on muscular power and performance during short-duration, high-intensity exercise. In the context of napping after a normal night of sleep, it’s unclear whether napping improves jump performance, while napping does not appear to improve performance during the 30-second Wingate test.^[10] However, one study reported that napping increased knee extensor maximal voluntary isometric contraction.^[11]

There is one study to consider in the context of napping after partial sleep restriction. This 2019 study was very similar to the summarized study and had resistance-trained men undergo partial sleep restriction (3 hours of sleep per night) for two nights, take a 1-hour nap (or no nap) at 1 p.m., and perform handgrip strength tests and 3 repetitions at 40%, 60%, and 80% of 1-repetition maximum for the bench press and inclined leg press at 5 p.m.^[12] In contrast to the summarized study, it was found that napping improved muscular power and velocity, as well as handgrip strength, compared to not napping. The reason for these conflicting findings is unclear, although a potential candidate is the greater sleep restriction in this study (3 vs. 4 hours of sleep per night), thus increasing the magnitude of napping’s potential benefit on performance.

In summary, napping tends to improve physical and psychological performance and reduce fatigue, whether it follows a night of partial sleep restriction or normal sleep. However, the effects of napping on specific measures of physical performance, such as power and maximal strength, requires further investigation, as the currently available evidence is limited and conflicting.

A limitation of this study is the absence of a control group that did not undergo partial sleep restriction. Another limitation is that objective measures were not used during the nap to assess the quality of sleep.